Methadone maintenance clients who continue substantial use of illicit opiates present a problem to treatment personnel. There is no generally accepted, specific treatment for these persons. The objective of this proposal is to assess the effectiveness of a dose manipulation strategy involving blockade, stabilization and contingent dose reduction designed to assist these clients to reduce heroin use. Approximately 50 clients identified by clinic staff as being at risk of involuntary termination from the program because of continued opiate use will be requested to participate in a 4 week baseline monitoring period during which they will not be at risk of termination. They will be paid for one additional urine specimen per week during baseline at $2 per specimen. Clients completing baseline will be requested to participate in a 10 week experiment and a 4 week follow-up period. The moratorium on involuntary termination and the payment for leaving one additional specimen weekly will be continued during the experiment and follow-up period. 40 clients who have agreed to participate will be randomly assigned to an experimental or a control group. Control group subjects will receive standard maintenance treatment for 10 weeks, but will have no changes in dosage. Experimental group subjects will be placed on a 10 week dose regimen in which their dose will be increased, stabilized and then decreased contingent upon provision of opiate-positive urine specimens. Dependent variables are number of opiate-positive specimens, attrition from the experiment, and termination from treatment. Treatment group differences in outcome will be examined by analysis of various techniques.